The qualified rate announced by the water department fights with the test result data of the CDC; The by-products produced by chlorine disinfection may be harmful, and this problem also exists in other big cities; Shenzhen water department mastered the new and safer technology more than ten years ago, but it was not popularized in the whole city.

Wang hengjia

Bao Jing in-depth investigation department reporter Wang Hengjia

On August 2, 2012 1 day, Shenzhen Water Network announced the full analysis and testing of the water discharged from the factory in July by the Municipal Water Quality Testing Center, with as many as 103 related standards. The test results show that all the factory water in Shenzhen meets the standard.

20 1 July1After the new Hygienic Standard for Drinking Water was implemented nationwide, Shenzhen Water Group announced in a high-profile manner that all projects in Shenzhen had passed the test in 2007. "The qualified rate of the new national standard for water quality of subordinate waterworks is all 100%." "Some indicators are far superior to the new national standard limit."

For some media, Shenzhen Water Group said: People think that the poor water quality is caused by the aging of the pipe network. ...

Accordingly, many insiders broke the news to Bao Jing reporter: 1. A state department recently came to Shenzhen for investigation, and several water plants in Shenzhen had projects exceeding the standard and were ordered to rectify by "interview"; 2. The water quality report published by Shenzhen Water Affairs Department for many years has some problems such as unreliable data; 3. The disinfection process used in many water plants in Shenzhen will produce disinfection by-products such as "trihalomethane", which may cause serious harm to human body if accumulated to a certain extent.

Three claims were disclosed, the first one was not confirmed for various reasons, and the last two were found to have certain factual basis through investigation by Bao Jing reporters. ...

Relevant surveys show that disinfection by-products "exceed the standard"

From 2007 to now, the monthly Bulletin of Urban Water Supply Quality published by Shenzhen Water Affairs Department basically claims that "the qualified rate of water samples leaving the factory is 100%". However, the survey results of other professional organizations are not the same.

From 2007 to 2009, experts from Shenzhen Center for Disease Control and Prevention conducted three surveys. The results show that the qualified rates of the effluent of urban waterworks are 82.9% and 84.5% respectively. 93% and 85. 0%.

In these three surveys, in addition to various conventional data, a similar problem was mentioned: disinfection by-products were mentioned as "exceeding the standard" twice and "higher than other cities" three times. This problem is quite strange to most citizens.

"In fact, this water is good all over the country."

So, what are the disinfection by-products? The reporter interviewed Huang, an authoritative expert on tap water disinfection in China, a professor at Harbin Institute of Technology and a doctoral supervisor.

Huang said that when the "raw water" used in the waterworks is relatively clean, it is no problem to disinfect with chlorine, but if the raw water is polluted and there are some organic substances, various disinfection by-products will be produced: trihaloids, MX and so on. Although the content of these by-products is not large, most of them are mutagenic, that is, when they reach a certain concentration or accumulate in human body, they may be mutagenic, carcinogenic and teratogenic.

So, are disinfection by-products in Shenzhen tap water harmful to human body? Huang said that if "mutagenicity" is positive, there is a possibility of carcinogenesis and teratogenesis, and the size of the possibility or harm needs further inspection and judgment.

From May to June, 2008, several experts from Shenzhen Center for Disease Control and Prevention conducted a "genotoxicity" study on the effluent from six water plants using "Dongjiang water" and "reservoir water". The mutagenicity of organic compounds in water samples was detected and compared by "Salmonella typhimurium mutagenicity test", "micronucleus test" and "micro-fluctuation test" respectively. The conclusion is that "the organic matter in the effluent of six water plants has obvious mutagenic effect, mainly frame-shifting mutation;" The results of micronucleus test and Ames test on genotoxicity of organic matter in water are basically the same. "

This study was published in academic journals, and other papers published around 20 10 also confirmed this point. The conclusion is that the mutagenicity of factory water is positive.

The reporter contacted one of several experts, who confirmed that the six water plants studied were all water plants in Shenzhen, and then said, "This issue is very sensitive. Everyone is drinking this water. If you do this thing, the water plant will be in trouble. In fact, this water is good all over the country. Our animal experiments do have results, but the impact on people needs epidemiological investigation to finally explain. Many animals are more sensitive than people, and there are still differences between people and animals. " After several days' consideration, she refused to interview in person.

The reporter interviewed a researcher from the Environment Institute of China Center for Disease Control and Prevention, who had conducted a nationwide tap water survey and visited Shenzhen many times. The researcher said that if you want to speak freely, you must be anonymous, and the pen name is Researcher Pi. Researcher Pi agrees with Huang: any mutation test that is positive may cause harm to human body. Moreover, chlorine disinfection is mainly used in several big cities in China, and there are more or less similar problems.

Huang expressed doubts about the data of trihalogenates detected by Shenzhen Water Monitoring Center. He said that he learned that the Shenzhen Water Affairs Department used the "headspace method" to increase the temperature and other conditions, "let the trihalogenates in the water run to the liquid level, and the liquid level is very large", so the measurement is not accurate. Liquid-liquid extraction method must be used for accurate measurement. For example, Huang said that he had done experiments himself. The water sample that can't be detected by "headspace method" and has no problem at all is detected by liquid-liquid extraction method, but it exceeds the national standard.

Researcher Pi said that at present, the country has formulated relevant standards for disinfection by-products, such as trihalomethane, but this does not mean that it is absolutely harmless as long as it is qualified. Disinfection by-products are lower than the relevant standards, and it is not uncommon to detect mutagenicity. At present, the country is not very strong in doing mutation experiments. "In order to keep their jobs, the leaders of local water departments should do more than one thing. If they can't, they won't do it. "

The tap water of the six factories involved in the paper failed the food safety assessment procedure?

Although there are no relevant detection standards and procedures for mutagenicity detection of tap water, there are food safety aspects.

According to the Rules for Toxicological Evaluation of Food Safety (GB15193.1-2003), the evaluation test is divided into four stages, the second stage is genotoxicity test, and the relevant provisions are: "From Ames test or V79/HGPRT gene mutation test; Micronucleus test of bone marrow cells or chromosome aberration test of mammalian bone marrow cells; Choose one from mouse sperm abnormality analysis or testicular chromosome aberration analysis respectively ... Among the three tests, one or more tests are positive in vivo and in vitro, indicating that the test subjects are likely to have genotoxicity or carcinogenicity, and generally should give up food application. If one of the three tests is positive in vivo or two are positive in vitro, two alternative tests (at least one in vivo) will be selected. If all the re-selected tests are negative, you can continue the next toxicity test ... "

After the revision, the Food Safety Toxicology Evaluation Rules (Draft for Comment) which has not been officially promulgated stipulates that "if two or more tests in the genotoxicity test combination are positive, it means that the test object is likely to have genotoxicity and carcinogenicity, and the food application should generally be abandoned."

Ames test and micronucleus test of effluent from six water plants were positive. That is to say, if the factory water used for the test is used as food, it is very likely that it will not pass the safety test in the second stage, let alone the third and fourth stages.

So, what can be done to solve the problem of disinfection by-products?

Huang said that he is familiar with the disinfection of tap water in Shenzhen. As far as he knows, chlorine dioxide disinfection in some water plants in Shenzhen is not real chlorine dioxide disinfection, but real chlorine dioxide disinfection can solve the problem of disinfection by-products.

Huang said that at present, 80% of water plants in Europe are using chlorine dioxide. This disinfectant is very safe.

The reason why some manufacturers in Shenzhen who use chlorine dioxide disinfection are still "positive" is probably because the chlorine dioxide hair growth technology they use is a "composite method", which produces a lot of chlorine gas at the same time. It is chlorine, not chlorine dioxide, that ultimately leads to positive results. Huang said that at present, China's relevant standards are being planned. Once introduced, the "composite chlorine dioxide generator" will be renamed as "chlorine dioxide and chlorine mixed generator".

Researcher Pi said that according to his own research, "the ratio of chlorine dioxide and chlorine gas produced by the compound chlorine dioxide generator is 1: 1 in theory, but actually it is 1: 2, which means that chlorine dioxide is only 33%."

Researcher Huang Hepi's statement can also be found in an internal document of Shenzhen Water Group.

Huang said that the concentration of chlorine dioxide produced by a real chlorine dioxide generator is above 95%. He used this generator for several years in many places for different water quality experiments, and the results showed that the "mutagenicity" of the factory water was negative.

Then, using chlorine dioxide as disinfectant will also produce some disinfection by-products? Huang said chlorite and chlorate would be produced. Under the condition that the water quality is not particularly dirty, the addition of pure chlorine dioxide is only 0.2 mg-0.5 mg/L, even if all chlorine dioxide reacts, it will not exceed the national standard. Repeated tests of this content are within the harmless range.

Researcher Pi believes that in a few cases, the dosage of chlorine dioxide may still exceed 1 mg/L, but even if it exceeds the national standard, chlorite and chlorate can be well removed, and simple follow-up processes can be added. Trihalomethane is a by-product of chlorine disinfection, which is difficult to remove. Of course, it can also be removed by further treatment such as activated carbon, but the cost will be higher and it will not be used in large water plants.

So, do experts in Shenzhen water department know the difference between chlorine dioxide and chlorine disinfection? According to the investigation of Bao Jing reporter, as early as 12 years ago, Shenzhen water affairs department made a special study on this.

Shenzhen found a solution to the problem of disinfection by-products as early as 200 1.

The reporter found a book in the library: chlorine dioxide purification technology for drinking water, which was published in June 2003. The editor-in-chief of the book is the current chief engineer of Shenzhen Water Group, and the editor is You, the current director of Shenzhen Water Group Technology Research Institute. The reporter contacted Zhang Jinsong and expressed his wish to interview him. He agreed at first, but later said that only the group approved it.

The preface of the book says, "Since the discovery that chlorine disinfection can lead to the production of' three-caused' compounds such as trihalomethane and haloacetic acid, the by-products produced by chlorine disinfection and its harm have attracted more and more attention." The book also lists the research in the United States and other countries, and tells the harm of these by-products to human body.

The preface also says, "In developed countries, chlorine dioxide has been widely used to purify drinking water." "Shenzhen Science and Technology Bureau has set up a scientific research project on chlorine dioxide purification of micro-polluted source water, which is jointly undertaken by Shenzhen Water Affairs Bureau and Shenzhen Water Affairs (Group) Co., Ltd., and the project has passed the expert acceptance on February 200165438+".

Page 10 of the book says that "chlorine dioxide has strong selective oxidation ability and broad-spectrum and efficient sterilization ability, and almost no organic by-products of chlorine disinfection are produced in the process of water purification ... chlorine dioxide has been produced and applied in drinking water purification in many countries, becoming one of the best alternative disinfectants for chlorine."

So, have they studied the difference between pure chlorine dioxide generator and "compound chlorine dioxide generator"?

On page 244 of the book, when studying a water plant using a "compound chlorine dioxide generator" in Shenzhen, it was written that "the composition analysis of the chlorine dioxide mixture generated by the generator (before entering the raw water) shows that the percentage of chlorine is slightly higher than that of chlorine dioxide." On page 262 of the book, it is written that "chlorine dioxide generators are divided into two categories: one is chlorine dioxide disinfectant generator, and the other is chlorine dioxide composite disinfectant generator ... chlorine dioxide disinfectant generator ... with a total score of not less than 95%."

Do they know that the mutagenicity of factory water is positive?

The two tables listed on page 244 of the book are the Ames test results of a water plant disinfected with chlorine and a water plant disinfected with "compound chlorine dioxide generator" in Shenzhen, and the results are all positive.

It is also pointed out in the book that even though the disinfectant produced by the "compound chlorine dioxide generator" contains a lot of chlorine, the mutagenicity of drinking water is "still low" compared with that of water plants that only use chlorine disinfection.

So, what is used for disinfection in the water plant in Shenzhen now? The explanation behind the Bulletin of Urban Water Supply Quality in June 20 12 issued by Shenzhen Water Network said that "water samples were disinfected with chlorine dioxide". The reporter counted 13 of the 46 water plants marked with "* *". According to insiders, many of these 13 used "*". According to industry insiders, the remaining 33 enterprises, except a few one or two that use ozone for disinfection, are still using chlorine for disinfection.

Experts believe that most water plants do not use chlorine dioxide because of the dispute between cost and benefit.

Why have you been aware of the benefits of pure chlorine dioxide, but you have been slow to use it?

The answers given by Huang Hepi include three items: 1. Habit; 2. Cost; 3. Interest disputes. They said that this is not a problem in Shenzhen, and big cities such as Beishangguang have similar problems.

Huang said that many waterworks leaders have the impression that chlorine dioxide is expensive and technically troublesome; After years of use, chlorine is cheap and convenient. In fact, at present, according to the calculation of chlorine dioxide 0.5 mg/L and chlorine 2 mg/L, disinfection with chlorine dioxide is only about 10 cents per liter of water. The dosage less than 0.5 mg/L may even be cheaper, and the technology is simple and easy to learn.

Huang said that several manufacturers that produced the "composite chlorine dioxide generator" before made a lot of money, with deep pockets and equipment maintenance benefits. It is difficult to replace them with pure chlorine dioxide generators.

Researcher Pi said that the chlorine dioxide disinfection technology in our country has been well promoted in waterworks below the county level, with some areas reaching more than 90%. Before the 2008 Olympic Games, Beijing thought chlorine gas was dangerous and might explode. It was very troublesome to use chlorine dioxide to train personnel, so it switched to sodium hypochlorite, which would not explode, but the disinfection by-products were still there. Beijing used it, and some places in Shanghai followed suit and used sodium hypochlorite.

As for the reasons why chlorine dioxide is easy to spread in small places and difficult to use in big cities, researcher Pi thinks: First, because big cities have traditions, some leaders dare not change the traditions and make mistakes themselves; Second, because small cities are far away from industrial centers, it is inconvenient to buy liquid chlorine, and big cities can get cheap liquid chlorine, and there are regular suppliers who supply it in large quantities every year, so there is a dispute of interests between them, which is difficult to break.

The facts involved in Bao Jing's previous report can explain some problems: Pingshan Water Supply Company bought a chlorine dioxide generator, and the family members led by the water supply company later set up a company to start producing chlorine dioxide generators and sold them to several neighboring water supply companies at high prices. Later, some manufacturers suspected that they were counterfeiting their patented products, so they sued. As a result, it is said that all chlorine dioxide generators have been abandoned and disinfected with recycled chlorine.

The book Chlorine Dioxide Purification Technology for Drinking Water, edited by Zhang Jinsong, has the following statement: "Because most water sources in China are in a state of mild pollution, when chlorine dioxide is used for disinfection, its dosage is generally above 0.5 mg/L, and the concentration of chlorite has exceeded the standard ... When chlorine dioxide is used for pre-oxidation, its dosage is generally around 2 mg/L ... A water plant in Shenzhen ... chlorite exceeds the standard by 0.5-2 times. However, adding new process measures will inevitably increase new investment and operating costs, which will undoubtedly reduce the application value of chlorine dioxide, which is slightly higher than chlorine in economy. "

According to the book, "the water purification cost of liquid stable chlorine dioxide with the highest cost is nearly 7 times that of chlorine gas, or even the lowest cost ... 24% higher than chlorine gas."

After 2002, He You also published many papers to discuss the control and removal of chlorite and chlorate, by-products of chlorine dioxide disinfection. There is a paper that "the concentration of chlorate produced in the process of drinking water purification will not be very high, and its harm will not become a big problem, so it should gradually fade out in the drinking water control standard." Another paper puts forward a process solution: "the concentration of chlorite may be in the state of exceeding the standard ... ferrous salt reduction method is a more environmentally friendly, economical and feasible method."

Researcher Pi analyzed the psychology of many water workers and said, "Chlorine dioxide is inherently expensive. If the water pollution is serious, it will be more expensive to increase investment. After the investment is increased, chlorite needs to be treated in the later stage to prevent it from exceeding the standard. Follow-up treatment is cheap, but it costs money. With chlorine, you can spend less money. Although some disinfection by-products will be produced, it is not easy to exceed the standard. Even if it exceeds the standard, you can't' not exceed the standard' by changing the detection method. In the case of not exceeding the standard, as for whether the test result is' positive', there is no compulsory test in the country anyway, which can be ignored. "

Direct drinking water in Meilin village 15 years ago was "absolutely safe".

As mentioned in the book "Chlorine Dioxide Purification Technology for Drinking Water", as early as 1998, Meilin Village adopted the treatment technology of ozone+activated carbon+ultrafiltration+chlorine dioxide, and the water can be directly drunk.

Up to now, the results of "Ames test" have not been published in the factory water of the whole city, but 15 years ago did the test in Meilin village, and the results were negative. At that time, the chlorine dioxide generator used in Meilin Village was an imported BELLOZON generator. This generator imported in 15 is not a "composite chlorine dioxide generator" used by many water plants in Shenzhen, but a "pure chlorine dioxide generator". According to Chlorine Dioxide Purification Technology for Drinking Water, the disinfection cost of pipeline direct drinking water in Meilin Village reached 0.497 yuan /m3.

Researcher Pi said that the water treated by these procedures is absolutely safe all over the world. This also shows that "Shenzhen water people have long known what to do", but it has not solved the problem of "for whom".

What should citizens do if they are worried about the water they drink? Some papers believe that when water is boiled for 5 minutes, the by-products of chlorine disinfection will drop to a low point.

Researcher Pi said: First of all, the water from some water plants in Shenzhen, such as Bijiashan Water Plant, is still very safe to supply water to the central area. Because even if there is chlorine, disinfection by-products can be removed by later advanced treatment, but the cost is high, and few water plants in Shenzhen use related technologies. Secondly, the public need not be too afraid, because there is also a process of accumulation of harm, but also the size of the incidence probability; Finally, if we attach great importance to the healthy treatment of water, if we have advanced treatment in the later stage, we will have to increase the cost of living and buy water purification equipment in the short term. Don't believe the false propaganda of some manufacturers when buying. The equipment doesn't need to be expensive. There are two key equipments: ultrafiltration and activated carbon. If you are only worried about disinfection by-products, activated carbon is enough.

data

100%

Shenzhen Water Network released data.

The Urban Water Quality Bulletin in May 2008, June 5438+February, July 2009 and June 5438+February all stated that the qualified rate of the factory water in that month was 100% according to the Hygienic Standard for Drinking Water (GB 5749- 2006). In the past few months, the effluent of 40, 43, 44 and 45 water plants were tested respectively.

82.9%

Investigation of experts in municipal and district centers for disease control and prevention

Among the 106 indicators tested, some water plants failed to meet the standards of turbidity, aluminum, manganese and residual chlorine.

The concentration of disinfection by-products in Shenzhen urban sewage is lower than the national standard, but higher than that in other cities ... The concentration of chlorite, chlorate, chloral trichloride, carbon tetrachloride and chloroform is relatively high, reaching more than 10% of the limit ... Attention should be paid to the control of disinfection by-products.

(In May 2008, experts from Shenzhen Center for Disease Control and Prevention studied the water samples from 35 water plants in Shenzhen (accounting for 72.9% of all water plants). The water quality testing and result evaluation were conducted in accordance with Standard Test Method for Drinking Water (GB/ T 5750-2006) and Hygienic Standard for Drinking Water (GB 5749- 2006) respectively. )

Investigation of experts in municipal and district centers for disease control and prevention

84.93%

Of the 73 water samples, 14 were unqualified, and 1 1 water samples were unqualified. The main unqualified indicators of water quality are still conventional indicators, such as aluminum, turbidity, manganese, free residual chlorine and chlorate. "When the sum of the measured concentrations of chloroform, monochlorodibromomethane, monochlorobromomethane and tribromomethane in two water samples exceeds 1, it is determined that the trihalomethane in these two water samples exceeds the standard; Compared with other cities, the concentration of municipal water disinfection by-products in Shenzhen is higher than that in other cities.

(In September 2007 (wet season) and May 2008 (dry season), 35 urban waterworks were selected for monitoring. )

Investigation of experts in Municipal Center for Disease Control and Prevention

85%

The main unqualified index (unqualified rate) is aluminum (7. 5%), turbidity (5. 0%) and chlorine dioxide (2. 5%) and trihalomethane (2. 5%). There are 1 samples of chloroform, monochlorodibromomethane, monochlorobromomethane and tribromomethane, and the sum of their respective limit ratios is 1. 338 7, exceeding 1. Therefore, it is judged that the trihalomethane in the water sample exceeds the standard. Compared with other cities, the concentration of municipal water disinfection by-products in Shenzhen is higher than that in other cities.

In the wet season (May 26th, 2008 and July 4th, 2009) and the dry season (February 8th, 2008 and February 22nd, 2009), 80 factory water samples were collected from 10 urban waterworks. )